Catalysts for oxidizing furfural and preparation thereof



Patented Mar. 22, 1949 CATALYSTS FOR OXIDIZING AND PREPARATION THEREOFErik B. Nielsen, Chicago, 11]., assignor to The Quaker Oats Company,Chicago, Ill., a corporation of New Jersey No Drawing. Originalapplication May 13, 1944, Serial No. 535,565, now Patent No. 2,421,428,dated June 3, 1947. Divided and this application September 11, 1946,Serial No. 696,375

18 Claims. (Cl. 252-48282) The present invention relates to improvementsin catalysts for oxidizing iurfural, particularly while the same is invapor form, for the particular purpose of producing therefrom maleicanhydride and maleic acid, and to methods of preparing the same, being adivision of my application Serial No. 535,565, filed May 13, 1944, nowPatent No. 2,421,428, dated June 3, 1947.

It has been proposed to subject furfural in vapor form to oxidation bymeans of an oxygencontaining gas while passing the mixture of furfuralvapor in said gas at an elevated temperature over catalysts containingvanadium.

In. processes of that type, however, the yields 7 have not beenparticularly high, and the control of the process has been somewhatdiflicult. The particular difliculties have resided in the preparationand activation of the catalyst, and more particularly with the methodsof coating a suitable carrier with the catalyst. For instance, theconventional method of coating a carrier with a suitable catalyst hasbeen to stir and evaporate a suspension of the catalyst to dryness inthe presence of the carrier. Such a method, however, is open to theobjection that the vessel used in the coating operation is thussubjected to the abrasive action of the carrier with the resuit that thefinishedcatalyst becomes contaminated by material mechanically abradedfrom the material out of which the vessel is constructed. Suggestionshave been made to spray, for instance, an aqueous or other liquidsuspension of a catalyst on to the carrier particles and then toforce-dry the thus sprayed carrier particles. An alternative proposalhas been first to preheat the carrier particles to such an extent thatthe suspension when sprayed thereon will be dried upon. contact with thecarrier as a result of the heat of the latter. The most seriousobjection to such a spraying procedure, however, is that it is difficultif not impossible, particularly in the case of catalysts containingsuspended materials, to produce an even spray. Moreover, the connectionsbetween the supply tank and the spray nozzle tend to become plugged bysettling out-of the suspended material with the result that the spray isuneven, with resulting unevenness and lack of uniformity of thecatalyst.

In accordance with the present invention a number of new steps are takenin order to pro- '2 vide a suitable catalyst for the vapor phaseoxidizing or iurtural. Among the objects of the invention are:

The production of a catalyst for the vapor phase oxidation of furfuralwhich comprises forming a catalyst and its promotor on a supportingmaterial and activating the thus supported catalyst by the passage ofoxygen-containing gas thereover at a temperature which is from about 10to 50 C. higher than the temperature at which the catalyst will be usedfor effecting the desired oxidation;

The process of activating a catalyst of the type already mentioned inwhich the activation is carried out in passageways or in a containerprovided with a nickel surface;'

The process of coating a carrier with a catalyst suitable for the vaporphase oxidation of furfural which comprises the steps of producing anaqueous suspension of the catalytically active materials, andemulsifying into said suspension liquid furfural, thereby thickening thesuspension, and admixing the resulting heavy emulsion with the carrier,and then drying the mixture and activating the same;

The process of producing a catalyst for the vapor phase oxidation offurfural which comprises producing an aqueous suspension of a suitablepromoter, ior example, iron molybdate, and then adding ammoniummetavanadate, ammonium molybdate and phosphoric acid neutralized withammonia to the suspension, dispersing furfural in the suspension toproduce an emulsion, and then admixing the resulting emulsified prodnetwith an inert catalyst carrier, drying the mixture and activating theresulting coated carrier and the catalyst held thereon by heating thesame for a prolonged time at a temperature within the range of fromabout 270 C. to 320 C. in a current of an oxygen-containing gas.

A catalyst formed in the manner described.

Other objects of the present invention will become apparent from thefurther description and the hereunto appended claims.

Thus I have found that particular advantage resides in forming thecatalytic materials in a suspension and then converting the saidsuspension into an emulsion by the addition of furfural. Such anemulsion may then be admixed with a suitable carrier which can then bespread out and allowed to dry at room temperatures. Such drying does notproduce any visible degradation of the emulsion.

Moreover, it has been found that if a promoter is to be incorporatedwith the catalyst, such promoter is far more eiiicacious if it isinitially formed in the suspension in which the catalyst itself isformed. Such formation of the promoter in the catalyst suspension istermed, in accordance with the present invention, as forming thepromoter in situ, so as to contrast it with the mere physical admixtureof the promoter with the suspension of the catalyst. It was found that apromoter produced in situ yields a catalyst which cures at a much fasterrate than an otherwise entirely similar catalyst in which the promoterhad been separately prepared and then added as a finely divided powderto the other catalyst components. It will be realized by those skilledin this art that any procedure which will tend to shorten the length ofthe curing period is of great importance because catalysts of the typehere under discussion must be cured for a considerable length of timebefore they will produce the optimum yield of the desired oxidationproducts, for example, maleic anhydride and maleic acid.

Furthermore it has been found that, contrary to reasonable expectations,the curing time may be shortened by curing the catalyst at a temperaturewhich is above that at which the-cured catalyst, when used for the vaporphase oxidation. of furfural, will produce the optimum yields.

I have found that the surface of which the catalyst chamber or catalysttubes are made has a decided effect upon the yield of the desiredoxidation product. Thus, the same catalyst will produce about 25 percent higher yields of malelc acid or its anhydride from furfural whenthe chamber has a nickel surface instead of a steel or iron surface.

The catalysts comprised within contemplation of the present invention,in general, may be considered as consisting of reaction products of theheating of a mixture of ammonium metavanadate and ammonium molybdatetogether with ammonium phosphate and an excess of ammonium hydroxide;the catalyst being further improved by the presence of such promoters asaluminum hydroxide, iron hydroxide, iron phosphate, iron molybdate,various oxides of arsenic, boric acid, alkalies such as potassiumhydroxide or sodium hydroxide, or alkaline earth hydroxides such as areexemplified by calcium hydroxide. A mixture of the various promoters maybe used. Moreover, the catalyst can be further improved by the presencetherein of a reaction product produced by incorporating ammoniumtungstate therewith.

While the exact composition of the catalyst I defies analysis, it caneasily be defined in terms of the chemicals or chem cal compounds whichare employed in its production. Where phosphoric acid is mentioned inconnection with the production of these catalysts, it is to beunderstood that the said phosphoric acid is first neutralized to litmusby means of ammonium hydroxide, whereafter the mixture is rendereddecidedly alkaline with ammonium hydroxide. A catalyst may, forinstance, be made from 20 parts of ammonium vanadate, parts of ammoniummolybdate, 5 parts of ammonia-neutralized phosphoric acid, an excess ofammonium hydroxide, and about 0.2 part of aluminum hydroxide. (All partsare by weight.)

Another example is one made from 20 parts of ammonium vanadate. 10 partsof ammonium molybdate, 3.4 parts of ammonia neutralized phosphoric acid,an excess of ammonium hydroxide, and 5 parts of iron phosphate.

Another example is a catalyst prepared from 20 parts of ammoniumvanadate, 5 parts of ammonium molybdate. 5 parts of ammonia-neutralizedphosphoric acid, 10 parts of ammonium tungstate, 5 parts of ironmolybdate, and 1 part of arsenic trioxide.

A further example is a catalyst prepared from 200 parts of ammoniumvanadate, 50 parts of ammonium molybdate, 1'? parts ofammonianeutralized phosphoric acid, 10 parts of boric acid, and 1 partof potassium hydroxide.

Still another example is a catalyst made from 20 parts of ammoniumvanadate, 5 parts of ammonium molybdate, 1.5 parts ofammonia-neutralized phosphoric acid, 10 parts of ammonium tungstate, and1 part of boric acid.

A particularly good catalyst, however, may be prepared in accordancewith the following example, which is to be considered as the preferredform in connection with the present invention,

and which is given in greater detail in order to set forth the variousadvantages to be derived from the formation of the promoter, in thiscase iron molybdate, in situ, as already mentioned, while the examplealso demonstrates the advantages accruing from the formation of afurfural emulsion from the suspension of the catalytic and promotingmaterials. The preferred catalyst 'therefore is prepared as follows:

24.5 parts by weight of ferric nitrate (Fe(NOs)s9I-Ia0) are dissolved in50 parts by weight of water. In a glass, glass-lined or ceramic vesselthere is also prepared a solution by dissolving 21.5 parts of ammoniummolybdate ((NHOsMorOu, 4Hz0) in parts by weight of water. Instead of theferric nitrate already referred to, any other soluble ferric salts maybe used. In any event, the solutions of the iron salt and of theammonium molybdate are mixed with each other, resulting in the formationof a canary yellow suspension of iron molybdate. The iron molybdate inthis case is the promoter. Into this suspension there is thenincorporated, while thoroughly mixing, a dry mixture consisting of 200parts by weight of ammonium metavanadate, and 50 parts by weight ofammonium molybdate. After this mixture has been incorporated with theiron molybdate suspension there is then added 200 parts by weight of a28 per cent solution of ammonia, whereupon 50 parts of 85% phosphoricacid, which has in advance been neutralized to litmus with ammoniumhydroxide, is introduced into the thus far formed suspension ofingredients. Into the alkaline-reacting suspension thus formed, parts byweight of furfural are gradually introduced with thorough agitation soas to disperse the furfural as a disperse phase in the suspension. Theresult of these operations is the formation of a heavy creamy emulsion.Into this emulsion there are then introduced 3000 parts by weight of aceramic carrier, of a size between 8 and 16 mesh. The incorporation ofthe carrier with the heavy emulsion produces granules thoroughly coatedwith the emulsion. The resulting mixture is then spread out thin uponsuitable supports which must not be made of iron, and the mixture isthen allowed to dry at room temperature.

This produces the desired catalyst which, howanhydride.

ever, still requires curing and activation. To accomplish this, 250parts of the dried catalytic material, that is to say, the carrier,coated with the catalytic material, are placed in a converter having anickel surface, whereafter air is passed over the material in theconverter at a temperature of about 300 C. for a period of 40 days. Atthe end of this activating or curing period the catalyst is then readyfor use as a vapor phase oxidation catalyst of furfural.

To produce maleic acid and maleic anhydride from this catalyst, forexample, a iurfural-air mixture containing about one per cent offuri'ural by volume, is preheated to the operating temperature for thecatalyst (270 C.) and passed over the catalyst at a rate so as to give acontact time oi'from about 0.2 to one second. The heat of reaction isremoved in heat exchange with a suitable medium such as Dowtherm" (whichis a mixture consisting essentially of diphenyl and diphenyloxide). Itwill be noticed that the tempei'ature at which the catalytic conversionis efl'ected is about 30 degrees lower than the temperature at which thecatalyst has been cured.

A catalyst prepared and cured in the manner I iiist described is capableof yielding as much as 71 per cent of theory of maleic acid and maleicAfter a two months operation the yield gradually increases to about 80per cent of theory and at the end of 300 days yields as high as 81 percent of theory have been obtained.

In order to recover the maleic acid or maleic anhydride, or both, fromthe eilluent flowing from the converter, the heated gases containing themaleic anhydride are passed upwardly through a suitably packed tower,for instance, one iilled with small porcelain Raschig rings, while wateris allowed to pass downwardly counter-current to the ascending gases.This water will dissolve the maleic anhydride, yielding a solution ofmaleic acid which may then be collected and from which maleic acid andmaleic anhydride can be recovered by ways well known to those skilled inthe art to which the present invention relates.

In order to demonstrate the value of formin the promoter in situ.comparisons have been made between a catalyst prepared as just describedin. connection with the preferred example using the same proportions ofmaterials, except that the iron molybdate, instead of beingprecipitated, as described in the preferred example, was separatelyprepared, filtered from its mother liquid, washed and dried, and thenincorporated with the other ingredients by being stirred into thesuspension of the ammonium metavanadate, ammonium molybdate, andneutralized phosphoric acid plus excess ammonium hydroxide. Moreover,the catalyst thus prepared was spread over a suitable support, dried,and cured in the same manner. At the end of 60 days. however, a catalystthus made was capable of yielding only about 53 per cent of theory ascompared with about.

75 percent of theory (average) of a catalyst which had been prepared inaccordance with the prefered example, i. c. with the promoter formed insitu.

In order to demonstrate the value of curing the catalyst at atemperature higher than that at No. 4 at 350 0., and No. 5 at 875 C. Inall cases the curing period was one month. The catalysts thus preparedwere tested for their ability to produce maleic acid and maleicanhydride. The results were as follows: Catalyst No. 1 yielded 62% oftheory: catalyst No. 2 (the one cured at 300 C.) produced 72% oi theory;catalyst No. 3 yielded 68% of theory; catalyst No. 4 yielded 52% oftheory; and catalyst No. 5 yielded only 33% of theory. This thereforeshows that temperatures not exceeding 325 C. are satisfactory, but thatwhen the temperature is above 325 C. the effect is deleterious. Inasmuchas 270 C. is the preferred temperature for the vapor phase oxidation ofthe iurfural to maleic acid and maleic anhydride. the temperature withinthe range of from 10 to 50 over and above that used for the catalyticconversion is suitable for the curing of the catalyst. In other words,this range has been demonstrated as beingcritical.

In order to demonstrate the importanceof the proper choice of thematerial to be used in the construction of the converter, two converterswere made of identical design, but one was made from aluminum and theother'from steel. Each was charged with the same amount of catalyst fromthe same batch. The catalysts were cured in the identical manner andthen after 60 days they were tested for their ability to convertfurfural into maleic acid and maleic anhydride. The aluminum converterwas capable of producing 58 per cent of maleic acid, while the one inwhich steel tubes were used produced only 42 per cent. Using an aluminumconverter on the one hand and comparing it with the steel converter, theinterior of which has been sprayed with 18-8 stainless steel,

' gave a yield of about 58 per cent which was the heating medium, forexample, diphenyl or a mixpasses over the catalyst. air is veryadvantageous as a carrier medium for ture of diphenyl and diphenyloxide, or some low melting metal which is a good heat transferringagent. It is also advantageous to preheat the air so that there will beno chilling effect as it Furthermore, heated introducing the furfuralvapor at a proper state which it will be used and also to show thecritical nature of the rather narrow rangeof tempera tures in which suchcuring can be efiected, five batches of catalyst, all prepared exactlyin accordance with the preferred example herein above given, were curedat the following temperatures: Noll at 270 C., No. 2 at 300 C., No. 3 at325 0.,

of dilution into the converter tubes.

Inasmuch as converters of this general type are well known, having beenused in connection with the oxidation of other organic substances invapor phase, for example, benzene, it is not believed necessary toillustrate these converters. In general they are of the type describedby C. R. Downs in U. S. Patent No. 1,604,739.

While the invention has been described in considerable detail,particularly in connection with one example, it is of course to beunderstood that this-is without intention in any wise to limit theinvention, beyond the scope of the pended claims.

AccordinglyI claim hereunto ap- 1, Catalyst for oxidation of furfuralwherein' the'catalytically active ingredients consist essentially of thereaction products resulting from 1 heating a mixture of ammoniumvanadate, ammonium molybdate, ammonium phosphate, and ammonium hydroxideand containing a promoter. 2. Catalyst for oxidation of iuriural whereinthe catalytically active ingredients consist essentially of the reactionproducts resulting from heating a mixture of ammonium vanadate, am-

monium molybdate, ammonium phosphate, ammonium tungstate, and amoniumhydroxide and containing a promoter.

3. Catalyst for oxidation of furfural wherein the catalytically activeingredients consist essentially oi the reaction products resulting fromheating a mixture of about 20 parts oi. ammonium vanadate, about 10parts 01' ammonium molybdate, about 5 parts of ammonia-neutralizedphosphoric acid, an excess of ammonium hydroxide and about 0.2 part ofaluminum hydroxide.

4. Catalyst for oxidation of furfural wherein the catalytically activeingredients consist essentially of the reaction products resulting fromheating a mixture of about 20 parts of ammonium vanadate, about parts ofammonium molybdate, about 5 parts of ammonia-neutralized phosphoricacid, an excess of ammonium hydroxide and about 5 parts oi ironphosphate.

5. A catalyst for oxidation of furfural wherein the catalytically activeingredients consist essentially of iron molybdate, and the reactionproducts of ammonium phosphate, ammonia, ammonium metavenadate andammonium molybdate, activated by an oxygen-containing gas at atemperature within the range of about 270 C. to 320 C.

6. Process 01 producing a catalyst for the vapor phase oxidation ofiurfural which comprises forming the catalyst comprising ammoniummolybdate, ammonium vanadate, ammonium phosphate, excess ammonia, and apromoter on a supporting material and activating the catalyst by thepassage of heated oxygen-containing gases thereover at an elevatedtemperature.

7. Process of activating a catalyst comprising ammonium molybdate,ammonium vanadate, ammonium phosphate, excess ammonia, and a promotersuitable for the vapor-phase oxidation of iuriural which comprisesheating said catalyst in a converter having a nickel surface in contactwith the catalyst while curing said catalyst by the passage thereover ofan oxygen-containing gas.

8. Process of coating a carrier with a catalyst suitable for thevapor-phase oxidation of furfural which comprises the steps of producingan aqueous suspension of the catalytically active materials includingammonium molybdate, ammonium vanadate, ammonium phosphate, excessammonia and a promoter, emulsifying iurfural with said suspension,admixing the resulting emulsion with the carrier, and drying themixture.

9. Process of producing a catalyst for the vapor-phase oxidation ofiurfural which comprises producing an aqueous suspension of ironmolybdate, ammonium metavanadate, ammonium molybdate, ammonium phosphateand excess ammonia dispersing iurfural in said suspension to produce anemulsion, admixing the emulsion with an inert catalyst-carrier, dryingthe mixture, and activating the resulting product by heating the samefor a prolonged time to a temperature of from about 270 C. to about 320C.

in a current of an oxygen-containing gas.

10. The process of claim 9 in which the activation of the catalyst iseiiected in a confined date with the resulting suspension, spreading thesame on a suitable inert carrier, drying the same thereon and activatingthe thus coated carrier by the passage thereover of an oxygen-containinggas at a temperature of from about 270 to 320 C.

12. In the process of producing a catalyst for the vapor-phase oxidationof furiural to maleic acid and maleic anhydride the step of forming acatalyst-promoter precipitate in an aqueous suspension, adding ammoniummolybdate, ammonium vanadate, ammonium phosphate and excess ammonia tosaid aqueous suspension, coating an inert carrier with the resultingmixture.

and drying and activating the coated carrier.

13. A process of producing a catalyst for the vapor phase oxidation offuriural which comprises adding to a suspension of iron molybdate, amixture of ammonium metavanadate and ammonium molybdate, followed byammonium phosphate and ammonium hydroxide and thereafter drying andactivating with an oxygen containing gas.

14. A process for producing a catalyst for the vapor phase oxidation offuriural comprising the addition of ammonium metavanadate, ammoniummolybdate, ammonia and ammonium phosphate to a suspension of a promoterprecipitate, said precipitate having been formed in the suspension towhich the other ingredients are added and thereafter drying andactivating with an oxygencontaining gas.

15. The process of claim 14 in which ammonium tungstate is addedtogether with ammonium metavanadate.

16. A process of producing a catalyst for the vapor phase oxidation ofiuriural wherein the catalytically active ingredients consistessentially of ammonium vanadate, ammonium molybdate, ammoniumphosphate, excess ammonia and a promoter which comprises placing thecatalyst in a converter having a nickel surface in contact with thecatalyst and curing said catalyst in an oxygen containing gas at atemperature higher than the temperature at which the highest yield ofmaleic acid or anhydride from furiural is obtained.

17. Process of producing a catalyst for the vapor phase oxidation ofiuriural which comprises producing an aqueous suspension of ironmolybdate and ammonium metavanadate in the presence of excess ammoniaammonium molybdate and ammonium phosphate derived by the neutralizationto litmus of phosphoric acid by means of ammonium hydroxide, dispersingfur- Iural in said suspension to produce an emulsion, admixing theemulsion with an inert catalystcarrier, drying the mixture, andactivating the resulting product by heating the same for a pro longedperiod of time to a temperature of from about 270 C. to about 320 C. ina current of an oxygen-containing gas.

18. In the process of preparing a catalyst suitable for the vapor phaseoxidation of furfural to maleic acid and maleic anhydride the step whichcomprises producing the promoter for the catalyst in situ byprecipitating an aqueous soluble iron salt by means of a solublemolybdate to produce a precipitate of iron molybdate, incorporatingexcess ammonia ammonium metavanadate, am-

.monium molybdate and ammonium phosphate,

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,895,522 Punnett Jan. 31, 19332,142,678 Porter Jan. 3, 1939 2,260,409 Slotterbeck et a1. Oct. 28, 19412,294,130

Porter Aug. 25, 1942

